Fused deposition modeling (FDM) filaments made of recycled materials are desirable for environmentally friendly and sustainable manufacturing of prototypes and load-bearing components in many applications. We investigate the effect of FDM process parameters on the mechanical properties of 3D-printed parts made of recycled polyethylene terephthalate (rPET) filaments. Increasing the nozzle temperature from 230 degrees C to 260 degrees C improves the strength of the specimens by 100%. Using a raster orientation parallel to the loading direction improves the ductility by more an order of magnitude. Specimen orientation and infill ratio also influence the mechanical properties. The temperature and the orientation effects are related to the quality of fusion between the printed lines. A modified Gibson-Ashby model correctly predicts the strength as a function of the infill ratio. Through the optimization of process parameters, the mechanical strength of 3D-printed rPET structures can reach that of injection-molded PET, making FDM a suitable manufacturing technique for load-bearing applications.